1. Field of the Invention
The present invention relates generally to a vacuum holddown apparatus and method of operation and, more specifically to a cut-sheet print media vacuum holddown particularly useful for a hard copy apparatus, such as an ink-jet printer.
2. Description of Related Art
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, "vacuum induced force" is also referred to as "vacuum induced flow", "vacuum flow", or more simply as just "vacuum" or "suction".] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve throughput specifications. For example, it is known to provide a rotating drum with holes through the surface wherein a vacuum through the drum cylinder provides a suction force at the holes in the drum surface. [The term "drum" as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term "platen" can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, such as a common typewriter rubber roller; thus, for the purposes of the present application, "platen" is used generically for any shape paper holddown surface used in a hard copy apparatus.]
Generally in a hard copy apparatus implementation, the platen is used either to transport cut-sheet print media to a printing station of a hard copy apparatus, such as a copier or a computer printer, or to hold the sheet media at the printing station while images are formed (known as the "print zone"), or both. [In order to simplify discussion, the term "paper" is used hereinafter to refer to all types of print media. No limitation on the scope of the invention is intended nor should any be implied.]
One universal problem, particularly pertinent in the adaptation of a vacuum holddown to use in a hard copy apparatus, is the management of different sized paper. Open holes around the edges of a sheet smaller than the dimensions of the vacuum field across the platen surface results in vacuum losses for holding. In other words, too many exposed vacuum ports result in a loss of holding suction and the paper is not firmly adhered to the surface. Generally, known apparatus rely on an end-user manually switching operational functions to adjust the vacuum field to match the size of the paper in current use. The apparatus known in the art also often require a fixed position leading edge registration feature in order to implement various transport vacuum size switching.
There is a need for a vacuum holddown for sheet material transport that can automatically adjust to hold a relatively universal variety of sizes of materials. In a hard copy apparatus implementation, the paper transport system preferably should operate while being moved at a relatively high speed (e.g., for a drum rotating at a surface speed approximately 30-inches/second).